Optimizing pitch allocation in a cochlear implant

ABSTRACT

Errors in pitch allocation within a cochlear implant are corrected in order to provide a significant and profound improvement in the quality of sound perceived by the cochlear implant user. The disclosure provides a tool for determining the implant fitting curve for cochlear implant system to correct pitch warping. The method presents familiar musical tunes to determine the implant fitting slope (relative alignment). In addition, in one embodiment, speech sounds may be used to determine the offset of the fitting line (absolute alignment). The use of music and speech to determine the implant fitting curve (line) and the slope is facilitated by using techniques to implement virtual electrodes to more precisely direct stimuli to the location or “place” on the cochlea.

RELATED APPLICATIONS

The present application claims the benefit of priority of U.S.Provisional Patent Application Ser. No. 60/523,928, entitled “OptimizingPitch Allocation in a Cochlear Implant Using Simple Melodies”, filedNov. 21, 2003, which provisional application is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates to implantable neurostimulator systems,such as cochlear implants and, more particularly, to a method foroptimizing pitch allocation as implemented in a cochlear implant.

BACKGROUND

Prior to the past several decades, scientists generally believed that itwas impossible to restore hearing to the deaf. However, scientists havehad increasing success in restoring normal hearing to the deaf throughelectrical stimulation of the auditory nerve. The initial attempts torestore hearing were not very successful, as patients were unable tounderstand speech. However, as scientists developed different techniquesfor delivering electrical stimuli to the auditory nerve, the auditorysensations elicited by electrical stimulation gradually came closer tosounding more like normal speech. The electrical stimulation isimplemented through a prosthetic device, called cochlear implant, thatis implanted in the inner ear to restore partial hearing to profoundlydeaf people.

At present, very few cochlear implant patients are able to enjoy music.This is due, in part, to the fact that the cochlear fitting programsthat process delivery of certain sound frequencies through a selectedelectrode or electrodes do not compensate for errors in pitchallocation.

Within the cochlea, there are two main cues that convey “pitch”(frequency) information to the patient. They are (1) the place orlocation of stimulation along the length of a cochlear duct and (2) thetemporal structure of the stimulating waveform. In the cochlea, soundfrequencies are mapped to a “place” in the cochlea, generally from lowto high sound frequencies mapped from the apical to the basilardirection.

Mapping an electrode array in a cochlear duct to the correct audiofrequencies is complicated by differences in an individual's anatomy. Inaddition, the final implanted position of the electrode array tends tobe variable, which lends an arbitrariness to a mapping scheme between anelectrode contact and perceived sound frequency. Thus, an optimalfitting map between an electrode contact and a sound frequency can onlybe roughly estimated at the outset for each individual. The initialestimate typically is inaccurate for that individual.

Another complicating factor is that the position of each electrode isnot very precise, i.e., there are only a limited number of electrodes,e.g., numbering about 16 to 24 electrodes, spread along the length ofthe electrode array, inserted into one of the spiraling ducts of thecochlea. Hence, mapping to a “place” within the cochlea is not preciseand is limited by the resolution of the discretely placed electrodes.

SUMMARY

The present inventors recognized that an improved fitting tool wasneeded to better convey pitch information to a user of a cochlearimplant. The disclosed devices and methods address this need byproviding a fitting routine for determining the fitting line and slopeof a cochlear implant and electrode array. The disclosed devices andmethods further provide a tool for quickly and accurately correctingpitch allocation errors in fitting cochlear implants. The result permitsthe significant improvement in the perception of sounds so that patientsmay enjoy music and more accurately perceive sounds havingcharacteristic pitch information such as speech.

In some embodiments, the fitting tool takes advantage of the concept of“virtual electrodes” which permits stimulation to be directed moreprecisely to a “place” on the cochlea, which place may be betweenelectrodes. Such “in-between” stimulation is not feasible in aconventional cochlear system. The use of virtual electrodes allowsdirected stimulation to nearly an infinite number of places on thecochlea. One example for implementing virtual electrodes is by usingweighted current steering through two or more electrodes. Anotherexample for implementing virtual electrodes is by applying stimuli attwo closely placed electrodes in an alternating, time-multiplexedmanner, so that stimuli are presented at the two electrodesnon-simultaneously.

In one aspect, fitting a cochlear implant system includes implanting amulti-electrode array into the cochlea of a user, the multi-electrodearray having an associated implant fitting line that defines arelationship between cochlear places of implant electrodes andassociated audio frequencies; presenting variations of a musical melodyto the user through the multi-electrode array; allowing the user toselect a variation of the musical melody that most closely conforms to amusical melody as remembered by the user; and determining a correctslope of the implant fitting line of the multi-electrode array based onthe rendition of the musical melody selected by the user.

In another aspect, fitting a cochlear implant system includes fitting acochlear implant system is provided. The method comprises: (a)implanting a multi-electrode array into the cochlea of a user; (b)determining a best slope of an implant fitting line by repetitivelypresenting a musical tune to the user, while varying the slope of theimplant fitting line, through the multi-electrode array, wherein theimplant fitting line defines a relationship between cochlear places ofimplant electrodes and associated audio frequencies; (c) allowing theuser to select a tune with a particular implant fitting line slope thatis most like the tune as remembered by the user; and (d) determining anoffset of the implant fitting line relative to an intrinsic fitting lineof the user's cochlea by repetitively presenting a familiar sound to theuser, while varying the offset of the implant fitting line, through themulti-electrode array, and allowing the user to select a familiar soundwith a particular offset, such that the familiar sound with theparticular offset is most like the sound with the pitch as remembered,wherein virtual electrodes are implemented to precisely deliver stimulito places on the cochlea while delivering tunes or sounds to the user.

In another aspect, finding the slope of an implant fitting lineincludes: (a) implanting a multi-electrode array into the cochlea of auser; and (b) determining the slope of an implant fitting line byrepetitively presenting a musical tune to the user, but with differentslopes at each presentation, through the multi-electrode array andallowing the user to select a tune with a particular slope that is mostlike the tune as remembered, wherein the implant fitting line defines arelationship between cochlear places of implant electrodes andassociated audio frequencies, wherein virtual electrodes are implementedto precisely deliver stimuli to places on the cochlea while deliveringtunes to the user.

In another aspect, a cochlear implant includes: an implantable pulsegenerator; an electrode array having a multiplicity of electrodesconnected to the implantable pulse generator; means for generating amusical tune delivered through the electrode array with differentslopes; and means for implementing virtual electrodes.

In another aspect, fitting a cochlear implant system includes: (a)implanting a multi-electrode array into the cochlea of a user; (b)presenting a first musical melody to a user through the multi-electrodearray, the first musical melody comprising a series of notes, each notehaving a predetermined frequency and duration; (c) varying the frequencyof one or more of the notes of the first melody in a predeterminedmanner to present a second musical melody to the user, the secondmusical melody being a distorted version of the first musical melody,wherein the user perceives that the second musical melody conforms to amusical melody remembered by the user; and (d) adjusting an implantfitting line of the multi-electrode array based on the variation betweenthe first musical melody and the second musical melody, wherein theimplant fitting line defines a relationship between cochlear places ofimplant electrodes and associated audio frequencies.

In another aspect, fitting a cochlear implant system includes:implanting a multi-electrode array into a cochlea of a user, theelectrodes being positioned on the array to have a spatial relationshipwith associated audio frequencies corresponding to positions along theuser's cochlea; presenting two or more variations of a sound to the userthrough the multi-electrode array; allowing the user to select a desiredvariation of the sound; and, based on the variation selected by theuser, determining a correct fitting of the multi-electrode arrayrelative to the user's cochlea

The described methods and systems are suited for users of cochlearimplants who have past experience in hearing simple, musical tunes andremember such tunes. A disclosed feature is to provide a fitting toolthat can be used in patients who do not have formal musical training.Another feature is to provide a fitting tool that can be implementedwith a software program and that can be accomplished quickly andaccurately in a clinical setting.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a current stimulation waveform that defines the stimulationrate (1/T) and biphasic pulse width (PW) associated with electricalstimuli, as those terms are commonly used in the neurostimulation art;

FIGS. 2A and 2B, respectively, show a cochlear implant system and apartial functional block diagram of the cochlear stimulation system,which system is capable of providing high rate pulsatile electricalstimuli and virtual electrodes;

FIG. 3A schematically illustrates the locations of applied stimuliwithin a duct of the cochlea, without the benefit of virtual electrodes;

FIG. 3B schematically illustrates the locations of applied stimuliwithin a duct of the cochlea or other implanted location, with thebenefit of virtual electrodes; and

FIG. 4A shows a graph showing the intrinsic line E of an individual'scochlea that is defined by the relationship between cochlear location(“place”) versus the log(frequency of perceived sound);

FIG. 4B shows another graph showing an intrinsic line E and a implantfitting line D showing both lateral and absolute misalignment that canbe referred to as “pitch warping”;

FIGS. 5A, 5B, and 5C show example implant fitting lines of threeindividual patients having cochlear implants, demonstrating that implantfitting lines on an cochlear distance versus Log(perceived frequency)plot are approximately linear over a large part of the perceived audiofrequency range;

FIG. 6 shows a representation of the relationship between cochlear placeand perceived frequencies (notes);

FIG. 7 shows an intrinsic curve (line) and an implant fitting curve(line) that are laterally aligned, i.e., the slopes are matched, but inwhich the two lines are not absolutely aligned, i.e., they are offset;

FIGS. 8A and 8B present a flowchart that outlines one embodiment of amethod for determining the optimal implant fitting curve (line);

FIGS. 9A, 9B and 9C show intrinsic line K and implant fitting lines Land M, which latter two lines are corrected for slope but do not havethe correct offset relative to the intrinsic line K;

FIG. 10 shows an example software interface menu that may be used toimplement the disclosed methods;

FIGS. 11 and 12 show example software interface menus that may be usedto implement an iterative process to determine the slope of the implantfitting line;

FIG. 13 shows a flowchart for ascertaining which patients are candidateswho might benefit from the fitting tool; and

FIG. 14 shows a flowchart that outlines one embodiment of a method ofpitch allocation in a cochlear implant by presenting distorted versionsof melodies to a patient.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The following description is of the best mode presently contemplated forcarrying out the disclosed devices and methods. This description is notto be taken in a limiting sense, but is made merely for the purpose ofdescribing the general principles of the disclosed systems and methods.The scope of the described systems and methods should be determined withreference to the claims.

The present disclosure describes a tool to better determine the implantfitting curve (line) for a cochlear implant. Simple musical melodies areused to help properly map specific electrodes and/or “places” on thecochlea to corresponding perceived audio frequencies. This mapping canbe referred to as an “implant fitting curve (line)” and depends inparticular on the type of electrode array used, the type of cochlearimplant, and the individual's anatomical variation. When the implantfitting line is properly determined and implemented in a cochlearimplant system, the patient is able to experience a significantimprovement in the perceived quality of sound, particularly with musicand speech.

The present methods and devices sometimes use the concept of virtualelectrodes to deliver better quality sound by more accurately directingstimulation current to the location or “place” on a cochlea whichprecisely corresponds to the audio sound frequency that the stimulationis intended to convey. Stimulation currents can be more preciselydirected by employing the concept of virtual electrodes, such that theresulting perception appears to arise from the presence of a virtualelectrode located somewhere between two physical electrodes. One way toachieve virtual electrodes is by providing concurrent, weighted currentsat two electrodes. “Current steering” is thus achieved. Anothertechnique for achieving a virtual electrode is to rapidly andalternately stimulate two closely placed electrodes, referred tohereinafter as a “time-multiplexed”, non-simultaneous, presentation ofstimuli to implement a virtual electrode. Employment of such techniquesto achieve virtual electrodes, allows stimulus current to be directed toan almost unlimited number of locations or “places” within the cochlea.

It will be helpful first to provide an overview of the structure of acochlear implant system. Such overview is provided below in connectionwith the description of FIGS. 1, 2A and 2B.

FIG. 1 shows a waveform diagram of a biphasic pulse train. The waveformshown defines stimulation rate (1/T), pulse width (PW) and pulseamplitude as those terms are commonly used in connection with aneurostimulator device, such as a cochlear implant, a spinal cordstimulator (SCS), a deep brain stimulator (DBS) or other neuralstimulator. All such systems commonly generate biphasic pulses of thetype shown in FIG. 1 in order to produce a desired therapeutic effect.

A “biphasic” pulse generally consists of two pulses: a first pulse ofone polarity having a specified magnitude, followed immediately or aftera very short delay, by a second pulse of the opposite polarity havingthe same total charge, which charge is the product of stimulus currentmultiplied by the duration of each pulse or phase. It is believed that“charge balancing” can prevent tissue damage at the site of stimulationand prevent electrode corrosion.

FIG. 2A shows an example cochlear stimulation system that may be used.The system includes a speech processor portion 10 and a cochlearstimulation portion 12. The speech processor portion 10 includes aspeech processor (SP) 16 and a microphone 18. The microphone 18 may beconnected directly to the SP 16 or may be coupled to the SP 16 throughan appropriate communication link 24. The cochlear stimulation portion12 includes an implantable cochlear stimulator (ICS) 21 and an electrodearray 48. The electrode array 48 is adapted to be inserted within a ductof the cochlea. The array 48 includes a multiplicity of electrodes 50,e.g., sixteen electrodes, spaced along its length that are selectivelyconnected to the ICS 21. The electrode array 48 may be substantially asshown and described in U.S. Pat. Nos. 4,819,647 or 6,129,753,incorporated herein by reference. Electronic circuitry within the ICS 21allows a specified stimulation current to be applied to selected pairsor groups of the individual electrodes included within the electrodearray 48 in accordance with a specified stimulation pattern, defined bythe SP 16.

The ICS 21 and the SP 16 are shown in FIG. 2A as linked togetherelectronically through a suitable data or communications link 14. Insome cochlear implant systems, the SP 16 and microphone 18 comprise theexternal portion of the cochlear implant system and the ICS 21 andelectrode array 48 comprise the implantable portion of the system. Thus,the data link 14 is a transcutaneous (through the skin) data link thatallows power and control signals to be sent from the SP16 to the ICS 21.In some embodiments, data and status signals may also be sent from theICS 21 to the SP 16.

In a conventional cochlear implant system, as shown more particularly inFIG. 2B, at least certain portions of the SP 16 are included within theimplantable portion of the overall cochlear implant system, while otherportions of the SP 16 remain in the external portion of the system. Ingeneral, at least the microphone 18 and associated analog front end(AFE) circuitry 22 will be part of the external portion of the systemand at least the ICS 21 and electrode array 48 are part of theimplantable portion. As used herein, “external” means not implantedunder the skin or residing within the inner ear. However, “external” canalso mean within the outer ear, including in the ear canal or caninclude residing within the middle ear.

Typically, where a transcutaneous data link must be established betweenthe external portion and the implantable portions of the system, suchlink is realized by an internal antenna coil within the implantableportion and an external antenna coil within the external portion. Inuse, the external antenna coil is aligned over the location where theinternal antenna coil is implanted, allowing such coils to beinductively coupled to each other, thereby allowing data, e.g., themagnitude and polarity of a sensed acoustic signals and power to betransmitted from the external portion to the implantable portion. Note,in other embodiments, both the SP 16 and the ICS 21 may be implantedwithin the patient, either in the same housing or in separate housings.If in the same housing, the link 14 may be realized with a direct wireconnection within such housing. If in separate housings, as taught,e.g., in U.S. Pat. No. 6,067,474, incorporated herein by reference, thelink 14 may be an inductive link using a coil or a wire loop coupled tothe respective parts.

The microphone 18 senses acoustic signals and converts such sensedsignals to corresponding electrical signals and may thus be consideredan acoustic transducer. The electrical signals are sent to the SP 16over a suitable electrical or other link 24. The SP 16 processes theseconverted acoustic signals in accordance with a selected speechprocessing strategy to generate appropriate control signals forcontrolling the ICS 21. Such control signals specify or define thepolarity, magnitude, location (which electrode pair or electrode groupreceive the stimulation current), and timing (when the stimulationcurrent is applied to the electrode pair) of the stimulation currentthat is generated by the ICS. Such control signals thus combine toproduce a desired spatio-temporal pattern of electrical stimuli inaccordance with the desired speech processing strategy. Unlike earliercochlear implant systems, more recent cochlear implant systemsadvantageously confine such control signals to circuitry within theimplantable portion of the system, thereby avoiding the need tocontinually send or transmit such control signals across atranscutaneous link.

The speech processing strategy is used, inter alia, to condition themagnitude and polarity of the stimulation current applied to theimplanted electrodes 50 of the electrode array 48. Such speechprocessing strategy involves defining a pattern of stimulation waveformsthat are to be applied to the electrodes as controlled electricalcurrents.

Analog waveforms used in analog stimulation patterns are typicallyreconstructed by the generation of continuous, short monophasic pulses(samples). The sampling rate is selected to be fast enough to allow forproper reconstruction of the temporal details of the signal. An exampleof such a sampled analog stimulation pattern is a simultaneous analogsampler (SAS) strategy.

Turning next to FIG. 2B, a partial block diagram of a representativecochlear implant that may be used to implement the present methods anddevices is shown. More particularly, FIG. 2B shows a partial functionalblock diagram of the SP 16 and the ICS 21 of an exemplary cochlearimplant system capable of providing a high rate pulsatile stimulationpattern and virtual electrodes. FIG. 2B depicts the functions that arecarried out by the SP 16 and the ICS 21. It should also be pointed outthat the particular functions shown in FIG. 2B (dividing the incomingsignal into frequency bands and independently processes each band) arerepresentative of just one type of signal processing strategy that maybe employed. Other signal processing strategies could just as easily beused to process the incoming acoustical signal. The devices and methodsdescribed herein could still be used to provide added flexibility inspecifying the stimulation patterns and waveforms that are selected andused with such additional signal processing strategies.

A complete description of the functional block diagram of the cochlearimplant shown in FIG. 2B is found in U.S. Pat. No. 6,219,580 ('580patent), incorporated herein by reference. It is emphasized that thecochlear implant functionality shown in FIG. 2B is only representativeof one type of cochlear implant and is not intended to be limiting.

In the manner described in the '580 patent, the cochlear implantfunctionally shown in FIG. 2B provides n analysis channels that may bemapped to one or more stimulus channels. That is, as seen in FIG. 2B,after the incoming sound signal is received through the microphone 18and the analog front end circuitry (AFE) 22, it is digitized in ananalog to digital (A/D) converter 28 and then subjected to appropriategain control (which may include compression) in an automatic gaincontrol (AGC) unit 29. After appropriate gain control, the signal isdivided into n analysis channels, each of which includes a bandpassfilter, BPFn, centered at a selected frequency. The signal present ineach analysis channel is processed as described more fully in the '580patent or as is appropriate using other signal processing techniques andthe signals from each analysis channel are then mapped, using mappingfunction 41, so that an appropriate stimulus current of a desiredamplitude and timing, may be applied through a selected stimulus channelto stimulate the auditory nerve.

Two or more stimulus channels may be selected simultaneously with thestimulus current being dynamically weighted in an appropriate mannerbetween the two or more channels to effectively steer the current fromone stimulus location within the cochlea to another. The concept ofcurrent steering is taught in U.S. Pat. No. 6,393,325 ('325 patent),incorporated herein by reference, for use within a spinal cordstimulation system. However, current steering as taught in the '325patent, may be employed within any type of neural stimulation system,including a cochlear implant system. Additional features and advantagesof current steering are taught in International Publication Number WO02/09808 A1, based on International Application Number PCT/US00/20294,filed 26 Jul. 2000, also incorporated herein by reference.

Thus it is seen that the system of FIG. 2B provides a multiplicity ofchannels, n, wherein the incoming signal is analyzed. The informationcontained in these n “analysis channels” is then appropriatelyprocessed, compressed and mapped in order to control the actual stimuluspatterns that are applied to the user by the ICS 21 and its associatedelectrode array 48.

The electrode array 48 includes a multiplicity of electrode contacts 50,connected through appropriate conductors to respective currentgenerators or pulse generators within the ICS. Through thesemultiplicity of electrode contacts, a multiplicity of stimulus channels,e.g., m stimulus channels, exist through which individual electricalstimuli may be applied at m different stimulation sites within thepatient's cochlea or other tissue stimulation site.

While it is common to use a one-to-one mapping scheme between theanalysis channels and the stimulus channels, wherein n=m, and the signalanalyzed in the first analysis channel is mapped to produce astimulation current at the first stimulation channel, and so on, it isnot necessary to do so. Instead, in some instances, a different mappingscheme may prove beneficial to the patient.

For example, assume that n is not equal to m (n, for example, could beat least 20 or as high as 32, while m may be no greater than sixteen,e.g., 8 to 16). The signal resulting from analysis in the first analysischannel may be mapped, using appropriate mapping circuitry 41 orequivalent, to the first stimulation channel via a first map link,resulting in a first stimulation site (or first area of neuralexcitation). Similarly, the signal resulting from analysis in the secondanalysis channel of the SP may be mapped to the second stimulationchannel via a second map link, resulting in a second stimulation site.Also, the signal resulting from analysis in the second analysis channelmay be jointly mapped to the first and second stimulation channels via ajoint map link. This joint link results in a stimulation site that issomewhere in between the first and second stimulation sites.

The “in-between” site at which a stimulus is applied may be referred toas a “stimulation site” produced by a virtual electrode. Advantageously,this capability of using different mapping schemes between n SP analysischannels and m ICS stimulation channels to thereby produce a largenumber of virtual and other stimulation sites provides a great deal offlexibility with respect to positioning the neural excitation areasprecisely in the cochlear place that best conveys the frequencies of theincoming sound.

As explained in more detail below in connection with FIGS. 3A and 3B,through appropriate weighting and sharing of currents between two ormore physical electrodes, it is possible to provide a large number ofvirtual electrodes between physical electrodes, thereby effectivelysteering the location at which a stimulus is applied to almost anylocation along the length of the electrode array.

The output stage of the ICS 21 which connects with each electrode E1,E2, E3, . . . Em of the electrode array may be as described in U.S. Pat.No. 6,181,969, incorporated herein by reference. Such output stageadvantageously provides a programmable N-DAC or P-DAC (where DAC standsfor digital-to-analog converter) connected to each electrode so that aprogrammed current may be sourced to the electrode or sunk from theelectrode. Such configuration allows any electrode to be paired with anyother electrode and the amplitudes of the currents can be programmed andcontrolled to gradually shift the stimulating current that flows fromone electrode through the tissue to another adjacent electrode orelectrodes, thereby providing the effect of “shifting” the current fromone or more electrodes to another electrode(s). Through such currentshifting, the stimulus current may be shifted or directed so that itappears to the tissue that the current is coming from or going to analmost infinite number of locations.

Still with reference to FIG. 2B, it should be noted that the speechprocessing circuitry 16 generally includes all of the circuitry frompoint (C) to point (A). In prior art cochlear implant systems, theentire SP circuitry was housed in a speech processor that was part ofthe external (or non-implanted) portion of the system. That is, in suchprior art systems, only the ICS 21 and its associated electrode arraywere implanted, as indicated by the bracket labeled “Imp1” (for“Implant-1”). This means that in such prior art systems, the signalpassing through the serial data stream at point (A) is also the signalthat must pass through the transcutaneous communication link from theexternal unit to the implanted unit. Because such signal contains all ofthe defining control data for the selected speech processing strategyfor all m stimulation channels, it therefore has a fairly high data rateassociated therewith. As a result of such high data rate, either thesystem operation must be slowed down, which is generally not desirable,or the bandwidth of the link must be increased, which is also notdesirable because the operating power increases.

In contrast to prior art systems, a modern cochlear implant, such as theCII Cochlear implant system manufactured by Advanced Bionics®Corporation of Sylmar, Calif., advantageously puts at least a portion ofthe speech processor 16 within the implanted portion of the system. Forexample, a cochlear implant may place the Pulse Table 42 and arithmeticlogic unit (ALU) 43 inside of the implanted portion, as indicated by thebracket labeled “Imp2” in FIG. 2B. Such partitioning of the speechprocessor 16 offers the advantage of reducing the data rate that must bepassed from the external portion of the system to the implanted portion.That is, the data stream that must be passed to the implanted portionImp2 comprises the signal stream at point (B). This signal isessentially the digitized equivalent of the modulation data associatedwith each of the n analysis channels, and (depending upon the number ofanalysis channels and the sampling rate associated with each) may besignificantly lower than the data rate associated with the signal thatpasses through point (A). Hence, improved performance withoutsacrificing power consumption may be obtained with such a cochlearimplant.

Future generations of cochlear implant systems may incorporate more andmore of the speech processor 16 within the implanted portion of thesystem. For example, a fully implanted speech processor 16 wouldincorporate all of the SP in the implanted portion, as indicated by thebracket labeled Imp3 in FIG. 2B. Such a fully implanted speech processoroffers the advantage that the data input into the system, i.e., the datastream that passes through point (C), would need only have a ratecommensurate with the input acoustic signal.

Additional features made possible by the cochlear implant system shownin FIG. 2B or equivalents thereof and, which may be used in conjunctionwith the presently described devices and methods, allow the currentstimuli to be applied to the target tissue at fast rates and in a waythat more naturally elicits a stochastic firing of the target tissue, astaught, e.g., in U.S. patent application Ser. No. 10/218,645 (filed Aug.13, 2002); 10/218,616 (filed: Aug. 13, 2002); and 60/425,215 (filed Nov.8, 2002); and in International Patent Application Serial No.PCT/US01/25861 (filed Aug. 17, 2002), all of which applications areassigned to the same assignee as is the present application and all ofwhich applications are incorporated herein by reference.

Next, with reference to FIG. 3A, a diagram is presented to illustratethe location where a stimulus is applied when virtual electrodes areemployed. In FIG. 3A, three electrodes E1, E2 and E3 of an electrodearray are illustrated. A reference electrode, not shown, is alsopresumed to be present some distance from the electrodes E1, E2 and E3,thereby allowing monopolar stimulation to occur between a selected oneof the electrodes and the reference electrode. Bipolar stimulation couldlikewise occur, e.g., between electrodes E1 and E2, between E2 and E3,or between any other pair of electrodes.

The electrodes E1, E2 and E3 are located “in line” on a carrier 150, andare spaced apart from each other by a distance “D”. Each electrode iselectrically connected to a wire conductor (not shown) that is embeddedwithin the carrier 150 and which connects the electrode to the ICS 21(see FIG. 2A or 2B). The carrier 150 is shown inserted into a duct 52within tissue 54 that is to be stimulated. For a cochlear implantsystem, the duct 52 typically comprises the scala tympani of a humancochlea.

When a stimulus current is applied to electrode E1, the stimuluslocation in the tissue 54 is essentially the location 56, adjacent thephysical location of the electrode E1. Similarly, when a stimuluscurrent is applied to electrode E2, the stimulus location in the tissue54 is essentially the location 58, adjacent the physical location of theelectrode E2. Likewise, when a stimulus current is applied to electrodeE3, the stimulus location in the tissue 54 is essentially the location60, adjacent the physical location of the electrode E3. It is thus seenthat the resolution or precision, with which a stimulus may be appliedto the tissue is only as good as is the spacing of the electrodes on theelectrode array. That is, each stimulus location in the tissue 54 isseparated by approximately the same distance “D” as separates theelectrodes.

With reference to FIG. 3B, a diagram is presented to illustrate thelocation where a stimulus is applied when virtual electrodes areemployed, specifically by using current steering. The structure of theelectrode array and spacing between electrodes E1, E2 and E3 is the sameas in FIG. 3A. Thus, when a stimulus current is applied only toelectrode E1, the stimulus location in the tissue 54 is the location 56,the same as was the case in FIG. 3A. Similarly, when a stimulus currentis applied only to electrode E2, the stimulus location in the tissue 54is the location 58. Likewise, when a stimulus current is applied only toelectrode E3, a stimulus location in the tissue 54 is the location 60.However, through application of current steering, a stimulus current maybe shared, e.g., between electrodes E1 and E2 (and some other paired orreference electrode), and the effective tissue location where thestimulus is directed may be anywhere along the line 62 between points 56and 58. Alternatively, if the current is shared between electrodes E2and E3, the location in the tissue where the stimulus is directed may beanywhere along the line 64 between points 58 and 60.

To illustrate further, suppose a stimulus current having an amplitude I1is applied to the tissue through electrode E1 (and some referenceelectrode). The location within the tissue 54 where the stimulus wouldbe felt would be the point 56. However, if a stimulus current of only0.9xI1 were applied through electrode E1 at the same time that astimulus current of 0.1xI1 where applied through electrode E2, then thelocation within the tissue 54 where the stimulus would be felt would bea little to the right of the point 56, more or less somewhere on theline 62. If the stimulus current applied through electrode E1 continuedto be deceased while, at the same time, the current applied throughelectrode E2 were increased, then the location in the tissue where thestimulus would be directed would move along the line 62 from left toright, i.e., from point 56 to point 58.

Similarly, by concurrently delivering current stimuli at electrodes E2and E3, the location in the tissue where the effective stimulus would befelt would lie somewhere along the line 64, depending on the weightingof stimulus currents delivered at the two electrodes. This concept ofcurrent steering is described more fully in U.S. Pat. No. 6,393,325,incorporated herein by reference.

It is noted that the concept of virtual electrodes which directs astimulus to a location on the cochlear location or place is broadconcept. One method of implementing virtual electrodes is byconcurrently delivering stimuli at two or more electrodes. Another wayof implementing virtual electrodes is to present alternating stimuli attwo electrodes in a time-multiplexed manner. For example, a firststimulus current is presented at the first electrode, then a secondstimulus current is presented at the second electrode then, the firststimulus current is presented at the first electrode, then secondstimulus current is presented at the second electrode, and so on, in atime multiplexed sequence. The first and second stimulus signals areusually different, e.g., they have different amplitudes and pulsewidths.Such delivery of stimulation will be perceived as if a virtual electrodewere delivering a stimulus, which virtual electrode appears to belocated between the two physical electrodes.

When an electrode array is implanted into one of the ducts of a cochlea,the spatial frequency represented by each electrode contact of theelectrode array must correspond to the spatial frequency or “place”along the cochlea.

FIG. 4A shows the relationship between the cochlear place (mm) versusthe associated audio frequency (Hz) of that place. The line E isreferred to herein as the “intrinsic line” having an “intrinsic slope”for an individual cochlea. In the ear, each place along the cochleacorresponds to a specific perceived sound frequency. This relationshipbetween cochlear place and perceived sound frequency is different forevery individual, since no two cochleas are alike and the nerve wiringbetween the cochlea and to the brain is different for every individual.In addition, the implant fitting curve (line) which maps the cochlearplace or electrode place versus perceived audio frequency will also bedifferent for every individual. To properly perceive sounds, as producedthrough a particular cochlear system, including a specific electrodearray, the implant system must be “fitted” or “tuned” to accommodate theindividual anatomical differences, the particular configuration of theelectrode array, as well as its particular placement in the cochlea.

FIG. 4B shows two curves (lines), the lower line, E, represents theactual relationship between the cochlear place (mm) versus theassociated frequency of that place. The upper line, D, represents theimplant fitting line of the cochlear implant which is misaligned withthe intrinsic line (and slope) E. This misalignment is sometimesreferred to as a “pitch warping”.

Assume that a 2000 Hz incoming tone is picked up (or generated) by thecochlear system. The cochlear implant user then should perceive a 2000Hz tone. After the electrode array is implanted, a guess is made forwhat the correct implant fitting line D (including slope) should be.However, because of variability in an individual's anatomical cochlea,invariably the guessed fitting line D will not initially correspond tothe intrinsic line E, as shown in FIG. 4B. The goal is to adjust (tune)the implant fitting line D to overlap the intrinsic line E.

From FIG. 4B, it can be seen that stimulation must be applied at aslightly different cochlear place than was originally guessed to yield aperceived frequency of 2000 Hz. For instance, the electrode and cochlearplace to be stimulated is at about 11 mm for the intrinsic line D, notthe predicted 10 mm for the implant fitting line E. Such pitch warpingmakes enjoyment of music difficult. Note, however, that if the electrodearray position in the cochlea is altered slightly, either placed furtherinto the cochlea or slightly out from the cochlea, the relationship ofeach “place” along the electrode array would again change inrelationship. Thus, to determine the slope of the electrode array“place” along the electrode array and the corresponding audio frequency,the electrode array must be fixed during the fitting procedure.

The challenge is to match the fitting line D to the intrinsic line E. Itwould be ideal that when a 2000 Hz tone is presented through thecochlear system, that a perceived tone of 1700 Hz can be reported by theindividual. But, most individuals cannot discern with precision that atone is actually 1700 Hz and not 2000 Hz, unless the individual ishighly musically trained and has perfect pitch.

There is now described an elegant method for determining the implantfitting curve (line) and the slope of implant fitting line. But beforediscussing the method, some concepts are first explained.

FIGS. 5A-5C illustrate the concept that in order to properly formulate afitting procedure, the nature of the relationship between the cochlear“place” and perceived audio frequency must be understood. It has beendiscovered empirically, as shown in FIGS. 5A-5C that the relationshipbetween the cochlear place (mm) versus the Log(perceived audio frequency(Hz)) is approximately linear for a large part of the perceived hearingrange. It can be seen in FIGS. 5A-5C that with the electrode arrayimplanted into the cochlea, a slope, calculated as the change inelectrode distance or, alternatively, the cochlear place, over thechange in log (frequency) may be obtained. It is an important fact thata good percentage of the audio frequency band is remarkably linear on aX-Log(frequency) plot, as this fact is utilized in the fitting procedureof the present method.

Another important concept to understand is that if the proper fittingslope is determined, the relationship of musical tones in a simple tunewill be recognizable. With the correct slope determined and applied,even if the fitting line does not overlap the intrinsic line, a simplemusical tune can be recognized, as each note in relationship to othernotes in a tune will be in a harmonic relationship.

FIG. 6 represents, in a simplified way, the relationship of musicalnotes to cochlear place. The place on the cochlea corresponds to noteson a musical scale, as represented by notes on a piano scale. Thus, forthe appreciation of music, it is important to determine the correctimplant fitting slope or “relative alignment” which is parallel to theintrinsic line and intrinsic slope.

FIG. 7 shows a situation where the implant fitting line G and intrinsicline F have the same slopes. Thus, the implant fitting line and theintrinsic line are in relative alignment. Line F represents theintrinsic cochlear slope of the log(perceived sound frequency) versusthe cochlear place. Line G represents the implant fitting slope of therelationship between electrode position, e.g., the first electrode atthe proximal end of the electrode array, versus the log(perceived soundfrequency). As discussed, to appreciate music, it is only necessary toalign the implant fitting slope, line F, to have the same slope as theintrinsic line G. This is because the relationship of musical notes(tones) continue to remain in harmonic relationship between notes, eventhough there may be an offset between lines F and G, as shown in FIG. 7.

The offset, however, does determine the overall pitch of sound that isperceived. That is, the overall pitch of the sound may be either too lowor too high, if the implant fitting slope of line F is not perfectlyaligned with the intrinsic slope of line G. When there is amisalignment, such that line F is offset to the right of line G, theperceived sound may sound “pinched”, “squeaky” or “tinny”. If the Line Fis offset to the left of line G, the perceived sound may be described astoo low.

The effect of offset, i.e., error in absolute alignment, is particularlyimportant in sounds having a characteristic pitch. This is especiallytrue of human speech which has a recognizable overall pitch. Thepresence of an offset, for example, line F to the right of line G, cancause male speech to be too high or “squeaky.” This is not unlike theeffect of playback on a record player or tape recorder at too highspeed. Conversely, line F offset to the left of line G can cause male(or for that matter, female speech) to be too low and be perceived as aslow, low frequency drone. This is not unlike the effect of playback ona tape recorder at too low a speed.

With understanding of the relationship between the cochlear place andthe resulting perceived audio frequency, an implant fitting routine maybe formulated. The fitting routine must satisfy the following basicrequirements: (1) the method must be capable of being performed quicklyin a clinical setting and (2) the method must yield an accurate result.

The method described herein satisfies the above two requirements. Anembodiment of the present method may be summarized as comprising atleast two major steps: (a) determining the individual's fitting slope,using a particular electrode array by presenting tunes embodyingdifferent fitting line slopes and (b) determining the offset or lateralalignment of the implant fitting line by presenting a known sound havingcharacteristic pitch, e.g., speech.

An individual's implant fitting slope depends on the individual'sanatomy, the electrode array configuration used, and the position of theelectrode array relative to the cochlea. Determining an individual'simplant fitting line (including the slope), quickly and accurately, isnot a trivial task. At first glance, it would appear that providingvarious tones through the electrode array could be used to determine thefitting line, so that it matches the intrinsic line, as in U.S.Provisional Application 60/433,037, filed Dec. 11, 2002, whichapplication is herein incorporated by reference. Using audio tones toobtain the fitting slope, however, is best suited to the highlymusically trained individual, as such individuals are generally able todistinguish between different tones and convey such differences to aclinician.

The present disclosure uses musical tunes to determine the fitting slopeboth quickly and accurately in any individual, including non-musicallytrained individuals. The use of musical tunes to determine the slope isnot immediately obvious. A simple, familiar musical tune, however, is agood reference to use because the relationship of notes within such atune can be quickly assessed for whether the notes are “harmonic.” Anindividual, without musical training, can easily and quickly identifywhether a tune is too compressed, i.e., the frequency range is toocompressed, and therefore the notes sound too much alike or thefrequency range is too expansive, such that the notes are perceived tobe to far apart than remembered. In addition, when the tune is playedwith different fitting slopes, a patient can quickly assess whether onerendition of a musical tune, presented with a particular implant fittingslope, sounds better than another rendition presented with a differentimplant fitting slope. When the implant fitting slope is correctlydetermined, a musical tune will sound most like a remembered musicaltune.

The present method is notable because determination of the implantfitting slope of the implant fitting line does not require specialmusical training. A subject can quickly ascertain the relationship ofone note to the next simply by remembering what a particular tune, e.g.,“Twinkle-Twinkle Little Star” should sound like. Not only is the methodaccurate, but the method can be completed relatively quickly in aclinical setting because such musical melodies, presented with differentfitting slopes, can be quickly implemented with appropriate programmablesoftware. Because the method is based on the subject comparing apresented tune with her memory of the tune, the described methods areparticularly suited for those subjects that have had previous auditoryexperience. If the patient was pre-lingual at the onset of deafness,then the patient has not had the experience necessary to recognizefamiliar musical melodies and is not a candidate for this fittingmethod, as described further below.

In some embodiments, the method described herein takes advantage ofrecent developments in stimulation technique—that is, the concept ofvirtual electrodes. Without use of virtual electrodes it would bedifficult, if not impossible, to accurately stimulate the cochlear placeto represent or “play” a tune. This is because in a typical 8 to 22electrode contact array, the individual electrode contacts do notprovide the required resolution necessary to stimulate the appropriateprecise points on the cochlea. The employment of virtual electrodes,however, facilitates the precise stimulation required by the presentfitting method to use musical tunes as a probe.

The method is described in connection with the flow chart shown in FIG.8A and continuing in FIG. 8B. Each step in the method shown in FIGS. 8Aand 8B is summarized in a “block”. The relationship between the steps,i.e., the order in which the steps are carried out, is represented bythe manner in which the blocks are connected in the flow chart. Eachblock has a reference number assigned to it.

The method can be simplified into two major parts: (a) determining theslope of the implant fitting line that relates Log(frequency of sound)to the “place” or location along the cochlea (“relative alignment”) and(b) determining the offset of the implant fitting line (“absolutealignment”). It may be possible to simply perform part (a) withoutfurther proceeding to part (b) and this is included as one embodiment.The best fitting routine, however, is performed by including both parts(a) and (b).

Referring to FIGS. 8A and 8B, a simplified flowchart is provided whichfurther illustrates the method of quickly optimizing the fitting of acochlear implant. The starting point is step 70 within the ellipse. Thenext step is shown in box 71, where one electrode (or the frequencyassigned to that electrode) is picked as a starting locationcorresponding to the first note of a familiar song or tune. Thiselectrode can be used each time as the spatial or place location of thefirst note of a song or tune presented. It is emphasized that this isfor the sake of convenience, and that if desired, a place half way orsomewhere between the location of the two electrodes, e.g., a virtualelectrode location, can be chosen as the anchor location for the firstnote. The next step, indicated by box 72, is to pick a predeterminedslope, i.e., the slope of the graph Log(frequency) versus cochlearplace. While this slope can vary from individual to individual, apredetermined (guessed) slope can be chosen based on known averages ofintrinsic slopes of individuals. This, at least, provides a roughballpark slope of the implant fitting line as a starting point. Next, asshown in box 73, a familiar tune or song is chosen, such as, forexample, from a menu of tunes (songs) and the tune is presented to thepatient. In presenting the tune, each following note, based on thechosen slope, will be precisely presented on a cochlear location or“place” by implementing the concept of virtual electrodes.

As discussed, virtual electrodes may be created in at least twodifferent ways. First, virtual electrodes may be created by deliveringweighted currents to two electrodes such that the effect is perceived asan electrode somewhere in between the electrodes. Another possible wayto create virtual electrodes is to rapidly alternate stimulation in atime-multiplexed manner between two electrodes. In other words, astimulus is applied at electrode E1 and then, a very short duration oftime later, a stimulus is applied at E2 and then, a very short durationof time later, a stimulus is applied at E1, and so on. The effect ofsuch rapid, time-multiplexed delivery of stimulation is to create avirtual electrode having a “place” located somewhere between the spaceof E1 and E2. As explained previously, notes following the first anchornote of a tune will be presented ideally with virtual electrodes whichincreases the resolution of stimulus presentation on the cochlea.

Next, as shown in box 74, the implant fitting slope can be changed andthe same tune or song can be presented to the patient starting at thesame anchor electrode, with the same first note. The patient thencompares the original rendition of the tune with the second rendition tosee which one sounds more like the tune, as remembered by the patient.The patient can record which slope is better. At this point, the patientmay choose to stop if the rendition is sufficiently close to theremembered tune but, usually, more slopes are presented and morerenditions of the same tune are presented as represented by the returnarrow back to box 74 from decision box 75. Based on the last response,another slope can be interactively chosen and the same tune once againcan be played. In this iterative process, the values of implant fittingslopes presented should begin to converge to a best value of the fittingslope, where incremental changes to the slope do not improve the qualityof the tune as perceived by the cochlear implant wearer.

Perhaps the best analogy of the iterative fitting process fordetermining the implant fitting slope is to analogize to the procedurefor fitting eye glasses. The process for determining lens strength(diopters) is accomplished by presenting various lenses with variouslens strength in a manner to “zero in” on the optimal lens prescription.The method requires starting with a lens of a particular prescription.Another lens strength is picked and then the better of the two ispicked. Armed with this knowledge, a third lens may be selected andpresented, and so forth, until a final, best lens is determined. Thesame iterative converging process may be used to determine the correctimplant fitting slope.

Once no appreciable difference is detected between two very closeimplant fitting slopes, one of those slope values can be chosen. The“relative alignment” portion of the process is now complete. Asmentioned, it may be possible to simply perform the relative alignmentprocess without further proceeding to the “absolute alignment” process.The best fitting routine, however, is performed by including theabsolute alignment process, which is described beginning with the nextstep, shown in box 76 of FIG. 8B. In this step, a predetermined(guessed) offset of the implant fitting line is selected.

The offset is the error in absolute alignment, which is described inmore detail with reference to FIGS. 9A-9C, which illustrate error inabsolute alignment using graphed lines K, L and M. Note that the slopesare the same for each line and therefore there is no lateralmisalignment. FIG. 9B shows the intrinsic slope of line K for anindividual's cochlea, which slope relates the log(perceived audiofrequency) to the cochlear place. FIG. 9A shows a line L offset to theleft of line K. Line L is the fitting curve (line) of an implantedcochlear implant, with an offset error. It is expected that the overallsound perceived will have a lower pitched than remembered. FIG. 9C showsline M offset to the right of fitting curve (line) K. The overall soundperceived with fitting curve K will be higher pitched than it should beor remembered.

To eliminate this error in absolute alignment, another sound probe otherthan musical tunes is used. Musical tunes are not the best probes forcorrecting the offset because tunes do not have an intrinsic “correct”pitch. Tunes may be played in different keys, with different overallpitch, and yet may be recognizable as musical tunes because each note inthe tune remains in harmonic relationship to other notes in the tune.

Other sounds, however, are associated with a known pitch. For example, achirping bird, a cricket sound or rain drops falling or sea surf soundshave a characteristic pitch that can be remembered. The best sound touse as pitch reference, however, is human speech, not only because it isimportant, per se, to optimize the implant system to sufficiently conveyspeech, but also because the human hearing system, including theassociated nervous system, is especially sensitive to the pitch of humanspeech.

Referring again to FIG. 8B, indicated in box 76, a predetermined offsetis chosen. This predetermined offset can be a guess based on empiricaldata of averaged values of intrinsic lines of individuals, using theparticular electrode array and cochlear system. This guessed offset willbe applied to the first presentation of speech as shown in box 77. Nextas shown in box 78, the patient can compare the perception of speech toremembered speech. Obviously, if it is male speech, but the speechsounds more like female speech, the offset is incorrect. In that case,the offset of the implant fitting line must be adjusted leftward tolower the overall pitch.

If the offset is not the best one, the decision step 78 indicates areturn line back to box 76, in which the offset is adjusted and the samespeech, with the new offset value, is then presented for comparison, asrepresented in box 77. As shown by the step 78, a comparison of theoverall pitch of the previous speech with the current speech is againmade and a decision can be made to record the speech rendition with theparticular offset having the better or more natural sounding overallpitch. Based on this decision, another offset may be chosen returning tothe step in box 76 and the same speech may be presented in box 77. Theoffset value should converge to a value wherein further increments tothe offset become smaller and do not provide appreciable improvement inthe overall sound pitch. After step 78, when the best offset isdetermined, this last, best offset value can be used to determine theimplant fitting line. Thus, at the end of the method signified by stop79, the method will yield both a slope and an offset defining the bestimplant fitting line.

The basic steps described above are best implemented with usercontrolled software to make the process efficient and accurate in aclinical setting.

FIG. 10 shows an example of a menu interface to a computer softwareprogram that can be used to implement the steps presented in FIGS. 8Aand 8B. The menu interface can have, for example, a selection of tunes100, so that a patient can select a short, familiar tune used for theremainder of the fitting/tuning process. By selecting key 101, using acursor for example, the patient or software operator can play apredetermined number of notes, such as, for example, seven notes, of thechosen tune. On the other hand, by selecting key 102 a complete melodycan be played. Selecting key 103 increases the implant fitting slope,whereas selecting key 104 decreases the fitting slope. Key 105 isselected to indicate that a current step (slope) size is the “best sofar” among the renditions presented, that have different step (slope)sizes. Key 106 is selected to restart the entire fitting process. Otherparameters can be pre-programmed before the play. For example, Key 107may indicate the first or starting electrode. Key 108 may indicate theanchor point on the slope, the electrode, or cochlear place, about whichthe fitting line is rotated to change the fitting slope. The frequencyor note which is assigned to this anchor electrode or anchor cochlearplace may be kept constant throughout the process of determining thefitting slope.

FIG. 11 further illustrates an example implementation of the fittingprocess in which the best implant fitting slope is determined. Displaysor lights 120-123 may indicate what current step (slope) size is beingpresented. Keys 124, 125 may be selected to play the first 7 notes of afamiliar melody but at different fitting slopes. Keys 126-130 may beused by the patient or software operator to record which one of thepresented musical renditions associated with a given step (slope) sizeprovides the best musical result. Display 131 indicates the current tuneor melody that is being played.

FIG. 12 illustrates a continuation of the fitting process to determinethe best slope of the implant fitting line. Display 140 shows thetune/melody that has been selected. Displays 120′, 121′, 122′, and 123′indicate the tune having a particular slope value is being played. Key141 is selected, for example, to go back to a rendition having a largeroffset. The possible offsets shown are 2.5, 3, and 3.5. These indicatethat the slopes being presented at 2.5 and 3.5 are half-steps (slopes),after rendition 3 has been first chosen from FIG. 11. This process isuse to converge to the best fitting slope. The half-steps shown,however, are arbitrary values and other values of steps sizes withdifferent markings or labels may be used to indicate a musical renditionwith a particular offset value. After all three renditions 2.5, 3 and3.5 are played, one of them may be marked or recorded as the best byselecting one of the “Best so far” keys. This iterative process maycontinue further until the best slope is found.

The next step of the fitting process is to determine the fitting offsetto provide absolute alignment of the implant fitting line to overlap theintrinsic line. The same iterative process can be used as shown in FIGS.11 and 12 to converge to the best offset value, using the same speech(or another sound having a characteristic pitch) each time, butpresented with different offsets.

It is emphasized that FIGS. 10, 11, 12 represent only an example ofinterface menus that may be employed to implement the fitting method.Other types of menus may be used and such other implementations forcarrying out the present fitting method are within the scope of thepresent claims.

FIG. 13 provides a flowchart for determining which patient 200 iseligible to undergo a cochlear fitting using simple musical melodies.The first selection criteria is provided in box 210—does the patienthave auditory experience? If the patient was pre-lingual at the onset ofdeafness, then the patient has not had the experience necessary torecognize familiar musical melodies and is not a candidate for thisfitting method. The next selection criteria is provided in box 220,where it is determined whether the patient has musical memory. In otherwords, is the patient capable of recognizing musical melodies? If not,the patient is not a candidate. The third criteria, represented by box240, is whether the patient has sufficient spatial resolution. That is,if the patient cannot distinguish fine differences in the cochlea, i.e.,the place in the cochlea, because of a defect such as an insufficientdensity of viable ganglion nerve cells in the cochlea, then the patientis not a candidate. If all criteria is met, then the patient is acandidate, as represented by box 250.

In summary, there is described herein a solution to quickly andaccurately fit a cochlear implant in order to reduce pitch warping, sothat patients can enjoy music and enhanced speech. The method can besimplified into two major parts: (a) finding the slope of the relationbetween Log(frequency of sound) and the “place” or location along thecochlea and (b) finding the offset of the implant fitting line. It mayalso be possible to simply perform part (a) without further proceedingto part (b), and that would be included as an embodiment of the method,however, a particularly advantageous fitting can be performed byincluding both parts (a) and (b).

There is now described alternative method of optimizing the pitchallocation in a cochlear implant using simple melodies. Pursuant to thismethod, a simple melody is presented to a user fitted with a cochlearimplant. The melody comprises a series of tone bursts, each tone bursthaving a predetermined frequency and duration. The melody can be apredetermined melody that the user is likely to be familiar with throughmemory. For example, the melody can be “Mary Has a Little Lamb”, whichis a melody to which a large number of people have been exposed. Afterthe user listens to the melody, the user determines whether the melodyconforms to the user's memory of that melody. If the answer is yes, thenthe pitch allocation in the user's cochlear implant is likely optimizedor close to being optimized. However, if the melody does not soundcorrect to the user, then the pitch allocation in the user's cochlearimplant is likely incorrect. The user is then iteratively presented withdistorted versions of the melody with the frequencies of the tones inthe melody being distorted in a predetermined manner until the melodysounds “correct” to the user. It should be appreciated that the melodyin the distorted state will not sound correct to an independent listenerbecause the melody has been distorted. The program of the cochlearimplant is then adjusted such that the distorted melody sounds“incorrect” and the original, actual melody sounds correct. The amountof adjustment to the program is determined based on the amount ofdistortion that was presented in the melody. In this manner, theprogramming of the cochlear implant is corrected so that the originalmelody sounds correct to both the cochlear implant user and to theindependent listener who is not fitted with a cochlear implant.

This process is now described in more detail with reference to the flowdiagram shown in FIG. 14. Each step in the method shown in FIG. 14 issummarized in a block. The relationship between the steps i.e., theorder in which the steps are carried out, is represented by the mannerin which the blocks are connected in the flow chart. Each block has areference number assigned to it.

The process starts at start block 298 and then proceeds to the firstoperation, represented by flow diagram box 300. In this operation, thefrequency assigned to one electrode is picked as a starting locationcorresponding to the first note of a familiar melody. This electrode canbe used each time as the spatial or place location of the first note ofa song or tune presented. In the next operation, the melody is played tothe patient, as represented by flow diagram box 305 in FIG. 14.Initially, the melody is played in an original format without anydistortion to the notes of the melody. As mentioned, the tune comprisesa series of notes, or tone bursts, each tone burst having apredetermined frequency and duration that is known by a personperforming the process. The patient has previously been fitted with acochlear implant, which processes the received tone bursts andstimulates the cochlea pursuant to programming of the cochlear implant,which programming includes an implant fitting curve (line) that maps thecochlear place or electrode place versus perceived audio frequency, asdescribed above.

The next operation is represented by the decision box 310 in FIG. 14,where the patient determines whether the melody conforms to the melodyas remembered by the patient. The melody is deemed to sound “correct” ifthe melody conforms to the melody as remembered by the patient. If thepatient determines that the melody does not sound correct (a “No” outputfrom the decision box 310), then this is an indication that the cochlearimplant is mistuned, as the patient is actually hearing a differentseries of frequencies than those that are actually being delivered tothe patient.

In the event that the melody does not sound correct (i.e., it does notconform to the user's memory of the melody), the process then proceedsto the flow diagram box 315, where the notes of the melody are distortedor varied in a predetermined manner in an attempt to make the melody, aspresented by the cochlear implant, conform more closely to the patient'smemory of the melody. That is, the respective frequency of one or moreof the notes in the melody is varied in a predetermined manner with theresult being a distorted version of the original melody. The melody (inthe distorted format) is then delivered to the patient, as representedby flow diagram box 305. The goal is to distort the melody in such a waythat the distorted version of the melody sounds “correct” to thepatient. It should be appreciated that the distorted version of themelody will sound awkward or incorrect to an observer that is not fittedwith a cochlear implant or to an observer that is fitted with aproperly-tuned cochlear implant. The operations of delivering the melodyto the patient, distorting the melody, and then receiving feedback fromthe patient as to whether the distorted melody sounds correct isiteratively repeated until the distorted version of the melody conformsto the patient's memory.

Once the melody has been distorted in a manner such that it conforms tothe patient's memory of the melody, the programming of the patient'scochlear implant is then adjusted until the distorted version of themelody sounds incorrect and the original version of the melody soundscorrect, as represented by flow diagram box 320 in FIG. 14. The amountof adjustment to the implant is determined based on the amount offrequency distortion that was required to distort the melody so that itconformed to the patient's memory.

There is now described a particular method for distorting the notes ofthe melody in a predetermined manner pursuant to the operation of flowdiagram box 315. As discussed above, it has been discovered empirically,as shown in FIGS. 5A-5C, that the relationship between the cochlearplace (mm) versus the Log(perceived audio frequency (Hz)) isapproximately linear for a large part of the perceived hearing range.Pursuant to a melody distorting process, each note in the melody isdistorted or varied in a predetermined manner as defined by thefollowing equation, which describes the amount of frequency distortionof each note of the melody, with the notes being represented by the Logof their respective frequency. The equation is as follows:log(F[i])=log(fLoc)+k(log(fNote)−log(fNote0))where F[i] is the distorted frequency of the melody note that is beingdistorted, fLoc is a reference frequency that is equal to the frequencyassigned to the electrode that was picked as the starting locationcorresponding to the first note of the melody, fNote is the originalfrequency of the melody note prior to distortion, fNote0 is the originalfrequency of the first note of the melody prior to distortion, and k isa variable that is iteratively varied when presenting the melody to thepatient. Pursuant to the operation of flow diagram box 315, theforegoing equation is applied to each note in the melody to arrive at adistorted set of notes for the melody. It should be appreciated that theforegoing equation is exemplary and that the notes of the melody can bedistorted in other manners.

Further explanation of the equation is now provided. The first portionof the right hand side of the equation is related to fLoc, which is thefrequency of a reference electrode to which the melody is tied. Thesecond portion of the right hand side of the equation represents thedifference in frequency between the current note, fNote, in the melodyand the first note, fNote0, in the melody. If the equation is used todistort the first note of the melody, then fNote=fNote0, such that thefrequency of first distorted note in the melody is simply equal to thefrequency of the reference electrode, fLoc. Subsequent notes in themelody are distorted by the frequency difference (i.e., (fNote−fNote0))between the subsequent note and the first note in the melody multipliedby the factor k (which represents a correction factor that is varied)and summed with the frequency of the first electrode, fLoc. Thus, thevalue of correction factor k dictates the amount of frequency variationbetween the notes in the distorted melody. As k increases, the frequencyvariation between notes in the melody also increases, and vice-versa.Note that k is therefore similar to the inverse of the implant fittingslope. As the implant fitting slope increases, the frequency variationas a function of cochlear place decreases and vice-versa.

Thus, in the operation of flow diagram box 315, the notes of the melodycan be distorted pursuant to the above equation and the distorted melodypresented to the patient in the operation of flow diagram box 305. Thedistorted melody is presented to the patient with variations of thecorrection factor k. When the patient listens to the melody as distortedby a new correction factor k, the patient makes the determination as towhether the notes in the melody sound too close together in pitch orwhether the notes sound too far apart in pitch. If the notes sound tooclose together in pitch, then the notes are next distorted using ahigher value of correction factor k than previously used, whicheffectively magnifies the differences in frequency (i.e.,log(fNote)−log(fNote0)) between the notes in the melody. The value ofcorrection factor k is iteratively increased or decreased until themelody sounds “correct” to the patient. If, for example, the notes soundtoo far apart in pitch compared to a previous rendition of the melody,the notes are subsequently distorted with a lower value of correctionfactor k than previously used, which effectively reduced the differencesin frequency between the notes in the melody.

The process of distorting the notes in the melody, presenting thedistorted melody to the patient, and subsequently distorting the melodyagain until the melody sounds correct can be performed using a pluralityof reference electrodes as fLoc. For example, the melody can bedistorted a first time using the frequency mapped to electrode 1 asfLoc, distorted a second time using the frequency of electrode 2 asfLoc, and so one for various electrodes. This will permit the melody tobe presented to the patient at different locations in the electrodearray, which corresponds to different cochlear locations.

As mentioned, when the distorted melody sounds “correct” to the patient,this is an indication that the patient's cochlear implant is mistuned.This is because the patient is actually being presented with a distortedversion of the melody that actually differs from the original melody. Atthis stage in the process, pursuant flow diagram box 320, the frequencyto electrode mapping of the cochlear implant is adjusted such that thedistorted melody sounds awkward or incorrect to the patient and theoriginal melody sounds correct to the patient in that it conforms to thepatient's memory.

The electrode mapping can be adjusted by varying the implant fittingline of the cochlear implant by a factor inversely proportional to thecorrection factor k that was previously found to distort the melody in amanner that made the melody sound correct to the patient. As mentioned,the correction factor k is akin to the inverse of the implant fittingslope.

It should be appreciated that the slope of the implant fitting line doesnot have to be adjusted uniformly across the entire electrode array.Rather, the slope can be adjusted differently based on different regionsof the array. For example, the region of electrodes 1-3 can be adjustedin one manner, the region of electrode 4-6 in another manner, and so onto generate an adjusted frequency-to-electrode map. One additionalparameter that can be assigned in the frequency to electrode map is thefrequency assigned to the first electrode. One way to assign thisfrequency is to have the patient listen to familiar voices forvariations of frequencies assigned to the initial electrode. The patientcan then pick the frequency for which the voices sound most natural.This frequency is then assigned to the first electrode in the array.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the claims. Accordingly, other embodiments arewithin the scope of the following claims.

1. A method for adjusting a cochlear implant system, the methodcomprising: using an interface of a software program to presentvariations of a musical melody to a user through a multi-electrode arrayimplanted into the cochlea of the user, wherein the multi-electrodearray has an associated implant fitting line that defines a relationshipbetween cochlear places of implant electrodes and associated audiofrequencies; allowing the user to select at the interface a preferredvariation of the musical melody; and determining a correct slope of theimplant fitting line of the multi-electrode array based on the variationof the musical melody selected by the user.
 2. The method of claim 1,wherein presenting variations of the musical melody comprises presentingthe musical melody to the user with different slopes of the implantfitting line such that the user perceives different renditions of themusical melody.
 3. The method of claim 2, further comprising determiningan offset of the implant fitting line relative to an intrinsic fittingline of the user's cochlea, comprising: using the interface of thesoftware program to present variations of a familiar sound to the user,the variations achieved by varying the offset of the implant fittingline; and allowing the user to select at the interface a variation ofthe familiar sound at a first offset.
 4. The method of claim 3, furthercomprising using virtual electrodes to deliver stimuli to the cochlearplaces.
 5. The method of claim 4, wherein using the virtual electrodescomprises presenting weighted stimulus currents simultaneously at twoelectrodes.
 6. The method of claim 4, wherein using the virtualelectrodes comprises presenting time-multiplexed stimulus currents attwo closely spaced electrodes.
 7. The method of claim 1, whereinpresenting variations of the musical melody comprises varying thefrequency of one or more of the notes of the musical melody to presentdistorted versions of the musical melody to the user.
 8. The method ofclaim 7, wherein the selected variation of the musical melody comprisesa distorted version of the musical melody.
 9. The method of claim 7,wherein determining the correct slope of the implant fitting line of themulti-electrode array based on the variation of the musical melodyselected by the user comprises using differences in relative frequenciesbetween an original version of the musical melody and the selectedvariation of the musical melody to determine the correct slope.
 10. Amethod for adjusting a cochlear implant system, the method comprising:(a) determining a best slope of an implant fitting line of an implantedmulti-electrode array in the cochlea of a user, comprising using aninterface of a software program to present variations of a musical tuneto the user by varying the slope of the implant fitting line of themulti-electrode array, wherein the implant fitting line defines arelationship between cochlear places of implant electrodes andassociated audio frequencies, and allowing the user to select at theinterface a variation of the tune presented with a first implant fittingline slope; and (b) determining an offset of the implant fitting linerelative to an intrinsic fitting line of the user's cochlea, comprisingusing the interface of the software program to present variations of afamiliar sound to the user by varying the offset of the implant fittingline of the multi-electrode array, and allowing the user to select atthe interface a variation of the familiar sound at a first offset. 11.The method of claim 10, wherein the familiar sound presented in step (b)comprises human speech.
 12. The method of claim 10, wherein determiningthe best slope in (a) comprises using a converging process whereinfurther incremental changes to the slope do not yield appreciableperceived improvement in the quality of the musical tune presented, inwhich event the best slope has been found.
 13. The method of claim 10,wherein determining the best slope in (a) comprises presenting the firstnote in different variations of the musical tune (1) at a same electrodewithout using a virtual electrode or (2) at a same cochlear place usingthe virtual electrode.
 14. The method of claim 10, wherein determiningthe best slope comprises: storing different values of slopes of theimplant fitting line in a computer memory; and presenting the variationsof the musical tune using the different values of the slopes.
 15. Themethod of claim 10, wherein: the electrode array is placed in the user'sscala tympani; and the electrode array includes at least eight electrodecontacts with even inter-electrode spacing.
 16. The method of claim 10,wherein virtual electrodes are implemented to deliver stimuli to placeson the cochlea.
 17. The method of claim 16, wherein the virtualelectrodes are implemented by presenting weighted stimulus currentssimultaneously at two electrodes.
 18. The method of claim 16, whereinthe virtual electrodes are implemented by presenting time-multiplexedstimulus currents at two closely spaced electrodes.
 19. A method forfinding the slope of an implant fitting line, the method comprising:determining the slope of an implant fitting line of a multi-electrodearray implanted in the cochlea of a user, comprising using an interfaceof a software program to present variations of a musical tune to theuser with a different slope of the implant fitting line at eachpresentation through the multi-electrode array, and allowing the user toselect at the interface a variation of the musical tune with a firstslope, wherein the implant fitting line defines a relationship betweencochlear places of implant electrodes and associated audio frequencies.20. The method of claim 19, wherein presenting the variations of themusical tune comprises incrementally changing the slope of the implantfitting line until further incremental changes to the slope do not yieldappreciable improvement in the quality of the tune, in which event thebest slope has been found.
 21. The method of claim 19, wherein virtualelectrodes are implemented to deliver stimuli to places on the cochlea.22. A method for fitting a cochlear implant system, the methodcomprising: using an interface of a software program to present a firstmusical melody to a user through a multi-electrode array of a cochlearimplant system implanted in the cochlea of the user, the first musicalmelody comprising a series of notes, each note having a predeterminedfrequency; using the interface to present a second musical melody to theuser, wherein the second musical melody varies the frequency of one ormore of the notes of the first melody in a predetermined manner suchthat the second musical melody comprises a distorted version of thefirst musical melody; receiving at the interface a user selection of oneof the first musical melody and the second musical melody as preferableto the user; and adjusting an implant fitting line of themulti-electrode array based on the user selection, wherein the implantfitting line defines a relationship between cochlear places of implantelectrodes and associated audio frequencies.
 23. The method of claim 22,wherein: the first musical melody comprises an original version of awell-known melody; and the second musical melody comprises a distortedversion of the well-known melody.
 24. The method of claim 23, whereinadjusting the implant fitting line comprising causing the first musicalmelody to conform to the musical melody as remembered by the user. 25.The method of claim 22, wherein varying the frequency of the one or moreof the notes of the first melody comprises: assigning the frequency of afirst note of the first melody to a predetermined electrode of thearray; and varying the frequencies of subsequent notes in the firstmelody relative to the assigned frequency.
 26. The method of claim 22,wherein varying the frequency of the one or more of the notes of thefirst melody comprises: for all notes in the first musical melody,calculating a difference in frequency relative to the first note;multiplying the difference by a correction factor; and adding theproduct of the difference and the correction factor to the frequency ofthe first note to arrive at the second musical melody.
 27. The method ofclaim 26, wherein the correction factor represents the variation betweenthe first musical melody and the second musical melody.
 28. The methodof claim 26, further comprising: varying the correction factor toachieve additional distorted versions of the first musical melody; andusing the interface to present the additional distorted versions of thefirst musical melody to the user.
 29. The method of claim 22, furthercomprising varying an association between the one or more of the notesof the first melody and various electrodes in the array, wherein theimplant fitting line is adjusted differently based on a location of thevarious electrodes along the electrode array.
 30. A method for adjustinga cochlear implant system, the method comprising: using an interface ofa software program to present variations of a musical melody to a userthrough an implanted multi-electrode array, the multi-electrode arrayhaving an associated implant fitting line that defines a relationshipbetween cochlear places of implant electrodes and associated audiofrequencies, wherein presenting the variations comprises varying thefrequency of one or more of the notes of the musical melody to present adistorted version of the musical melody to the user; allowing the userto select at the interface a variation of the musical melody that mostclosely conforms to the musical melody as remembered by the user,wherein the variation of the musical melody that most closely conformsto the musical melody as remembered by the user comprises a distortedversion of the musical melody; and determining a correct slope of theimplant fitting line of the multi-electrode array based on the variationof the musical melody selected by the user.
 31. A method for adjusting acochlear implant system, the method comprising: using an interface of asoftware program to present variations of a musical melody to a userthrough an implanted multi-electrode array, the multi-electrode arrayhaving an associated implant fitting line that defines a relationshipbetween cochlear places of implant electrodes and associated audiofrequencies, wherein presenting the variations comprises varying thefrequency of one or more of the notes of the musical melody to present adistorted version of the musical melody to the user; allowing the userto select at the interface a variation of the musical melody that mostclosely conforms to the musical melody as remembered by the user; anddetermining a correct slope of the implant fitting line of themulti-electrode array based on the variation of the musical melodyselected by the user using differences in relative frequencies betweenan original version of the musical melody and the selected variation ofthe musical melody to determine the correct slope.